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Multiple births, not heart disease, is biggest IVF health risk

As far as the long-term health risk is concerned, the jury is still out

MAURO FERMARIELLO/SCIENCE PHOTO LIBRARY

By Michael Le Page

“Children born through IVF face a potential health time bomb.” “Assisted reproduction is an ‘evolutionary experiment’ that could prove as big a health disaster as junk food.” These were some of the claims that appeared in many newspapers last week, after evolutionary biologist Pascal Gagneux gave a talk at the American Association for the Advancement of Science meeting in Washington DC.

Gagneux claimed IVF increases the risk of heart disease and metabolic disorders, meaning children conceived in this way are more likely to suffer from, say, strokes or diabetes when they reach middle age. “We can’t rule out that it could be shortening lifespan,” he is reported as saying.

His claims are alarming and their phrasing insensitive, but is there anything to them?

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There is undoubtedly one major health risk associated with assisted reproduction – the increased chance of having twins, triplets or more. But this is the result of implanting multiple embryos to increase the chances of success rather than of IVF itself.

Many would-be parents see twins as a bonus. But multiple births are more dangerous for the mother, and the children are more likely to be born prematurely or have a low birthweight, and to suffer from lifelong physical and mental issues such as deafness, blindness or cognitive impairment.

For instance, a woman is twice as likely to die during a twin birth, and more than half of twins are born before 37 weeks. As a result, implanting only a single embryo at a time is becoming the preferred practice in many countries.

What about the health of children born singly after IVF? Overall, it seems much the same as that of children conceived conventionally. A 2013 review of the evidence to date described it as “reassuring”.

Lower birthweight

But IVF has not been around long enough to rule out problems emerging later in life – the first person born by IVF, Louise Brown, is not yet 40. IVF children do have slightly lower birthweights – a predictor of later health issues – and several studies do suggest children born after IVF have slightly higher blood pressure, higher blood sugar or are more obese, which would increase the risk of cardiovascular or metabolic disorders later on.

The most concerning studies come from Urs Scherrer of University Hospital in Bern, Switzerland, whose team has compared 65 IVF teens to a similar number conceived conventionally. The findings suggest the IVF children have a higher risk of cardiovascular disease later in life, says Scherrer, though it is not possible to put a precise figure on the risks.

“There are a lot of people who are quite concerned,” says developmental biologist Tom Fleming of the University of Southampton, UK, who has studied the effects of IVF on mice. But Fleming points out that other studies in mice have not found any effect on lifespan.

It is simply too soon to tell what will happen as people born by IVF reach their 40s and 50s, says Tessa Roseboom of the University of Amsterdam in the Netherlands, who studies the health effects of IVF. “We really don’t know yet,” she says.

Epigenetic changes?

Assuming future studies confirm that there is indeed an adverse effect on health, the question is why. There are many possible reasons.

For starters, IVF children are more likely to be an only child and to have older parents, so they may spend less time chasing siblings around the house. Any issues they have could also be a result of the health issues affecting the fertility of their mother, say, or the greater age of their father.

The work of Fleming and others, though, suggest that the heart problems are related to the culture medium in which developing embryos are grown for five days before being implanted. This seems to alter the epigenetic programming of embryos, which can have lifelong effects.

Culture media are currently selected solely on the basis of whether they increase the chance of women getting pregnant. They should instead be chosen on the basis of whether they boost the chances of a healthy child being born, says Roseboom.

This will not be easy, though, as many clinics buy their media from companies that do not reveal the concentrations of their ingredients. “We don’t have full disclosure,” says Daniel Brison of the University of Manchester, UK, whose group is tracking the health of children born by IVF.

The bottom line is that while there is some evidence that children born by IVF will have an increased risk of heart or metabolic disorders later in their lives, the jury is still out. Even if these fears are confirmed, there are treatments for cardiovascular conditions such as high blood pressure, Fleming points out, and the treatments might be much better by the time large numbers of children born by IVF start growing old. “It’s not panic stations,” he says.

With the exception of Scherrer, all the researchers New Scientist spoke to thought multiple births a much bigger health threat. That’s not a message that’s getting through to all would-be parents though, with fertility clinics reporting that many ask for two or more embryos to be transferred even after being told of the risks.